The in-band phase noise of a phase-locked loop circuit (PLL) can be heavily dominated by noise from a phase detector of the PLL circuit. Tri-state phase-frequency detectors (PFDs) are commonly used in PLL circuits as a phase detector for their ability to act as frequency detectors in addition to their ability to detect phase. However, tri-state PFDs can suffer from relatively large in-band phase noise.
Sub-sampling phase detectors (SSPDs) have also been used in PLL circuits as a phase detector. However, PLL circuits with SSPDs typically have a narrow locking range and disturbances can push the PLL circuits out of a locked state.
Accordingly, new circuits and methods for providing phase detectors are desirable.